1. Field of the Invention
The present invention relates to a gas insulated breaking device, and more particularly to silver plating which is formed on a slide contact portion with respect to a gas insulated breaking device which is used in a power transforming field of a power system.
2. Description of the Related Art
FIG. 1 is a side view showing the constitution of a puffer type gas insulated breaking device which includes an arc-extinguishing chamber of a two-directional blow method to which the present invention is applicable, and the basic constitution of the breaker has been well known as a related art.
In FIG. 1, the gas insulated breaking device is constituted of a grounded tank 12 in which a SF6 gas 11 which constitutes an insulating medium is sealed and a manipulation housing 14 which accommodates a manipulation device 13 therein, wherein a manipulation force is transmitted through a shaft seal 15. A driving force of the manipulation device 13 is transmitted by way of an insulation manipulation rod 17 which is accommodated in the inside of an insulation support sleeve 16 which is arranged in the inside of the grounded tank 12, wherein a movable arc contact 18 and a movable contact 19 are respectively mechanically separated from a fixed arc contact 20 and a fixed contact 21 thus performing the current breaking.
To establish the electric connection between a puffer cylinder 1 and a finger contact 2, the finger contact 2 is configured to slide on a surface of the puffer cylinder 1. To realize a favorable electrically connected state, silver plating treatment is applied to a slide portion. When a silver plating film is erased due to a progress of wear of the silver plating by sliding, the contact resistance of the slide portion is increased thus giving rise to a possibility that heat attributed to Joule heat is generated along with the supply of electricity.
To enhance the lubricity of the slide portion thus suppressing the increase of the wear of the silver plating and the contact resistance, a lubrication material is applied to the silver plating (see, JP-A-9-306326, Movable Contact Device of Circuit Breakers) being published as patent document of Japan ((page 3, FIG. 4), for example).
As shown In FIG. 4 in JP-A-9-306326, silver plating 21 is applied to a surface of a movable contact 9 which constitutes a base material of a slide portion. Further, to enhance the lubricity of a slide portion, binder 22 made of perfluoropolyether and graphite 23 are used as lubrication materials. These lubrication materials possess heat resistance of 400° C. or more and hence, the binder 22 can firmly hold the graphite 23 thus maintaining the favorable lubricity.
With respect to the slide portion of the gas insulated breaker which includes a breaker portion to which these lubrication materials are applied, the same silver plating film is arranged on surfaces of the puffer cylinder and the finger contact. Further, to enhance the lubricity of the slide portion, the binder made of perfluoropolyether and the graphite are used as the lubrication material.
As described above, due to the advantageous effect of the lubrication materials applied to the slide portion, the wear of the silver plating is reduced thus providing the structure which prevents the increase of the contact resistance. However, it is impossible to completely suppress the wear and it is necessary to perform the silver plating treatment with plating thickness corresponding to the slide condition required by the device. When members having different hardnesses slide with each other, the wear of the soft member having the low hardness progresses, and the hard member having the high hardness is hardly worn.
In the slide portion of the conventional gas insulated breaker, the silver platings which are manufactured by the same process are applied to respective surfaces of the puffer cylinder and the finger contact. In general, however, plating treatments of both parts are processed with lots different from each other and hence, there arises difference in plating hardness between these silver platings although the difference is trivial. Since which one of the plating film of the puffer cylinder and the plating film of the finger contact assumes a larger value depends on the number of manufacturing lots, it is not always possible to choose one of them.
In the observation after carrying out a slide test, following two cases exist in a mixed form. That is, in the first case, the silver plating on the puffer cylinder side is remarkably worn, while the plating on the finger contact side is hardly worn, while in the second case, to the contrary, the silver plating on the finger contact side is remarkably worn and the plating on the puffer cylinder side is hardly worn. Which one of both parts exhibits more wear in silver plating depends on the hardnesses of plating films of both parts. Since the hardnesses depend on the number of manufacturing lots, when the slide portion of an arbitrarily gas insulated breaker is taken as an example, it is difficult to determine which one of the plating film of the puffer cylinder and the plating film of the finger contact exhibits more hardness.
Accordingly, in the slide portion of the conventional gas insulated breaker, to prevent the increase of the contact resistance even when the plating film of either one of the puffer cylinder and the finger contact is worn, silver plating treatment of the same thicknesses is applied to both sides.
However, the part which is worn in an actual apparatus is either one of the plating film of the puffer cylinder and the plating film of the finger contact and hence, there has been a drawback that another plating film possesses an unnecessarily large thickness.
Further, as described above, the silver plating is required to satisfy functions which are contradictory to each other, that is, the realization of the favorable electrical contact state and the maintenance of the favorable slide state. While the realization of the favorable electrical contact requires the reduction of the contact resistance, the soft plating film is suitable for the realization of this function.
FIG. 3 is a schematic view which depicts the contact state of the slide portion microscopically. In general, when two surfaces are brought into contact with each other, fine projections which are present on the respective surfaces are brought into contact with each other and these fine projections are subject to the plastic deformation in response to pressing. The magnitude of the plastic deformation is controlled by a pressing pressure and hardnesses of members which are brought into contact with each other, wherein the plastic deformation of the soft film is larger than the plastic deformation of the hard film and a contact area of the soft film becomes larger than a contact surface of the hard film. Since the contact resistance is controlled by the contact area, the contact resistance of the soft film having the large contact area is decreased.
On the other hand, with respect to the sliding, the hard film is advantageous to the contrary. The reason that the silver plating is used in the slide portion of the gas insulated breaking device is that the silver plating film is originally soft and hence, is subject to large plastic deformation when the film is pushed whereby it is possible to expect an advantageous effect that the contact resistance is reduced.
Although the silver plating is worn due to the sliding between the puffer cylinder 1 and the finger contact 2, a wear quantity is generally controlled by hardness. That is, the harder the film, the wear quantity is decreased. Accordingly, when the silver plating is formed of the soft film, the wear attributed to sliding is increased and hence, there arises a drawback that it is necessary to preliminarily increase the thickness of the silver plating film and, at the same time, the worn powder constitutes metal foreign substances and lowers the insulation performance of the apparatus.
To the contrary, when the silver plating is formed of the hard film, although the wear quantity can be reduced, the contact resistance is increased. By applying the lubrication material which is constituted of the binder made of perfluoropolyether and graphite described as the related art to the soft film, it is possible to expect an advantageous effect to reduce the wear quantity to an extent. However, compared to the hard film, the wear quantity is still large and hence, the wear quantity reduction effect is not less than optimum.
Here, the soft film and the hard film, in general, correspond to the presence or the non-presence of a gross agent. In case of the silver plating having the basic composition, non-gross silver plating which is formed of the soft film is used. However, in case of the silver plating which uses following gross agents (1) to (7) listed below which are described in table 2. 70 on page 354 of “Hyomen Gijutsu souran, —mekki•youkyokusankahen— (book on surface technology-plating and anodization—)”, original version, Koshinsha Co., Ltd. Jun. 15, 1983, which is a non-patent document, due to the suppression of an electrochemical reaction attributed to the addition of a gross agent, the crystalline structure of silver is finely granulated and hence, a degree of surface smoothness is enhanced whereby the grossness is obtained. Since added substances and hydrogen are precipitated as impurities in grain boundaries of fine crystals, the hard plating film is obtained.    (1) condensation product of carbon dioxide and ketones    (2) xanthic salt    (3) ASK compound (acrolein-sulfur disulfide condensation product)    (4) thiocarbazide condensation product    (5) thio sulfate    (6) selenium and tellurium compound    (7) antimony-bismuth compound